You forgot to execute the query:
using (SqlCommand cmd = new SqlCommand("INSERT INTO dbo.Sources(SourceID, SourceName, Active) VALUES(@SourceID, @SourceName, @Active)", con))
{
cmd.Parameters.Add(new SqlParameter("SourceID", mSourceID));
cmd.Parameters.Add(new SqlParameter("SourceName", mSourceName));
cmd.Parameters.Add(new SqlParameter("Active", mActive));
cmd.ExecuteNonQuery();
}